Re: Concrete Ecologic Example Myth

[epirad@mchsi.com]

The points below answer your question, it is a myth to formulate a concrete 

example when your summary data is so poor.  What you are asking is for someone 

to explain why your data is so bad since you can't figure out why it is 

yielding an inverse association. 



You have a negative association between smoking and radon. Your lung cancer 

mortality rates do not accurately represent actual lung cancer incidence rates 

for the time period of interest. Lung cancer is co-correlated to the other SES 

variables by varying degrees within a county.



If you really need a concrete example, you could perform a series Monte Carlo 

analyses with varying degrees of correlation between the smoking data (within 

county) and confounding (SES) socioeconomic variables. I am not funded to do 

this and have many more pressing issues.  Better yet, use the methods I sent 

you to improve upon your analyses by looking at within group variation.  



But, we still disagree that you are even testing the LNT given all the non 

supported assumptions you made in deriving your own LNT formula.  All the 

asumptions you made in your derivation have led to your findings and the model 

mispecification. 









> 	I don't see why any of the discussion below prevents you from

> making up a concrete hypothetical example.

> 

> Bernard L. Cohen

> Physics Dept.

> University of Pittsburgh

> Pittsburgh, PA 15260

> Tel: (412)624-9245

> Fax: (412)624-9163

> e-mail: blc@pitt.edu

> web site: http://www.phyast.pitt.edu/~blc

> 

> On Fri, 20 Jun 2003 epirad@mchsi.com wrote:

> 

> > Kai,

> >

> > I know we have gone through discussions about the limitations of ecologic

> > studies many times but there are some points that a few radsafers continue to

> > miss.

> >

> > You suggested the other day putting an upper limit on the error from an

> > ecologic study.  Unfortuantely, this is not easy to do since the error in

> > ecologic studies is unbounded.

> >

> > Others problems to keep in mind -

> >

> > 1) It is not possible to identify empirical sources of ecologic bias from

> > aggregate data alone. Researchers must rely on prior knowledge of intergroup

> > variation in the distribution of other risk factors and effect modifiers.



> > We don't know this inter group variation for Dr. Cohen's data nor has he

> > adjusted for it.

> >

> > 2) Factors responsible for ecologic bias may not be confounders or effect

> > modifiers at the individual level and that identifying the bias is even more

> > difficult because factors may not even “appear” to be confounders or modifiers

> > at the ecologic level.

> >

> > 3) Ecologic biases can even reverse the direction of an observed association,

> > especially when the range of average exposure levels across groups is small or

> > the exposure under study is not a strong risk factor regardless even if you 

> are

> > using an ecologic study to test the LNT.

> >

> > 4) If cross level bias is occurring (which we know it is), ecologic data can

> > not be successfully used to adjust for ecologic bias.

> >

> > Many examples have been given on how Dr. Cohen's data can be biased and since

> > Cohen will use his own faulty data to test the "concrete" example; providing

> > a "concrete" example is doing no more than providing an explanation Cohen will

> > use his own faulty data to negate.  So, the circle will never end.

> > > Friends,

> >

> > > We are all aware that ecological studies have some limitations - these 

> issues have been discussed (some would say ad

> > > infinitum) on this board and elsewhere.

> >

> >

> 

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